Method of producing elastic yarn and product



Dec. 6, 1960 F. c. FIELD, JR 2, 6

METHOD OF PRODUCING ELASTIC YARN AND PRODUCT Filed March 29. 1954 FIG. 3

FIGZ

INVENTOR FREDERICK C. FIELD, JR.

ATTORNEY United States Patent METHOD OF PRODUCING ELASTIC YARN ANDPRODUCT Frederick C. Field, Jr., Wilmington, DeL, assignor to E. I. duPont de Nemours and Company, Wilmington, DeL, a corporation of DelawareFiled Mar. 29, 1954, Ser. No. 419,355

Claims. (Cl. 28-72) This invention relates to treatment ofcontinuous-filament yarn so as to provide improved bulkiness and otherdesirable properties in the yarn and in fabrics made therefrom.

Conventional yarns made of continuous filaments are notably deficient,as compared with staple yarns, in bulk, covering effectiveness, andinsulating ability, all of which impairs their usefulness for appareland other textile purposes. Breen patent applications S.N. 261,635 filedDecember .14, 1951 (now U.S. Patent 2,783,609) and S.N. 375,372 filedAugust 20, 1953, (now U.S. Patent 2,852,906) teach novel treatment of abundle of continuous filaments to form bulky yarn characterized byloopiness produced in the individual filaments upon passage through azone of turbulence. The present invention is dependent upon similarfilament-convoluting means, but whereas Breen clearly prefers to formthereby a configuration of loopy yarn capable of resisting appliedtensioning force, the present invention is directed toward formation ofan intermediate yarn configuration thereby that, also loopy, is looseand open, incapable of resisting appreciable force applied to extend theyarn. Further modification of the yarn according to this inventioncompletes the transformation to a highly desirable bulky yarn.

Aprimary object of the present invention is production of bulkycontinuous-filament yarn characterized by extreme extensibility undertension and recoverability after removal of the tensioning force.Another object is provision of yarn comprising continuous filrmentscontaining non-helical loops removable temporarily by extension of theyarn. Other objects will be apparent from the following description andthe accompanying diagrams.

Figure 1 is a schematic representation of apparatus useful according tothe present invention. Figure 2 is a front view of a jet or nozzleelement of the apparatus of Figure 1. Figure 3 is an exploded side viewof the apparatus of Figure 2. Figure 4 is a cross-sectional side View ofthe apparatus of Figure 2. Figure 5 is an enlarged view of multifilamentyarn after treatment by the apparatus of Figure 2. Figure 6 is a view ofthe yarn of Figure 5 after subsequent stabilization, extension, andrelaxation.

In general, the objects of this invention are accomplished by passingcontinuous-filament yarn through a zone of turbulence to form along thelength of each filament a multitude of loops susceptible to removal byextension of the filament, stabilizing the loops by exposure of the yarnto a setting treatment before extension, extending the yarn to distortthe loops, and then relaxing the yarn.

As shown in Figure l, yarn to be treated may be supplied from bobbin 1through pigtail guide 2, tension .guide 3, and pigtail i, to passsuccessively over canted roll 5, driven roll 6, into the nip of thedriven roll and drive roll 7, and back over the canted roll. Afterseveral 'passes over this three-roll combination, the yarn goes throughslub cleaner 8 and through jet or nozzle 9 into the nip of driven roll10 and drive roll 11, over canted 2,962,794 Patented Dec. 6, 1960 roll12, back through the roll nip, then over the rollers of tensiometer 13,through pigtail guide 14, setting tube 15, pigtail 16, over canted roll17, and through the nip of driven roll 18 and drive roll 19. Afterseveral passes about this roll combination the yarn passes about winduproll 22 driven by roll 24 after entering the nip of the rolls. Adjustingmechanism 21 ensures that windup drive roll 24 rotates at a greater ratethan drive roll 19 does, thus extending the yarn in this portion of itspath.

Details of the jet or nozzle 9 appear in Figures 2, 3, and 4. Housing 30holds casing 31 of tube 32 in bore 33 by means of screw 34 through side35 into threaded side 36 separated from the other side of the housing byslit 37. Screw 38 threaded into the top of the housing fastens clamp 39to hold venturi member 40 in place. Bore 41 through one side of thismember is extended as recess 42 in the opposite side at venturi throat43 to anchor the tube and permit adjustment to greater or less depth ofinsertion. Nut 44 at the entrance end of the tube casing carries ceramicinsert 45, and. for part of its length at the exit end is the tube ishalved along the axis or slitted, as shown. The nut is notched on theface parallel to the edges of the slitted end to ensure proper assemblywith the slit in the downstream direction. The venturi member has gasket47 about neck 48, while mouth 49 has hardened insert 5% recessed in it.Air or similar fluid enters the housing at intake 51, which isexternally threaded for connection to a suitable pressure source (notshown). The bulky or loopy form of continuous filament in the yarnpersists from the mouth of the jet to the third three-roll combination,as suggested in the drawing by a jagged-line representation of the yarnbetween these two points, whereas a smooth line represents the yarnelsewhere in this schematic diagram.

Yarn place at the entrance of the tube is carried through the tube andout the slitted end into the throat of the ven uri and out the mouththereof by concurrent flow of fluid. Expansion of the fluid, usuallyair, sepa-. rates the yarn componen s, and accompanying turbulencewhipsthem about violently. While any staple component is subject to partialor comnlete separation from the bodyof the yarn, continuous filamentcomponents loop and may be otherwise convoluted. Sufiicient entanglementof the loops to produce a relatively stable configuration that stronglyresists tension applied to the yarn is favored by a large number offilaments, high yarn twist, highpressure at the jet, and only a modestexcess of yarn supply rate over windup rate. However, all these featuresadd to operating costs, and the present invention is adapted especiallyto production of a bulky yarn by jet rocessing of low-twist yarn havinga relatively small number of filaments at low jet pressure and high netyarn overfeed.

In surface appearance a continuous-filament component of yarn processedthrough a jet according to this invention exhibits a multitude of ratherlarge loops loosely intermingled and apparently randomly distributedalong the len ths of separate filaments. Such loops appear in themultifilament yarn of Figure 5, which is distinguishable from yarndescribed in the above-mentioned Breen applications by greater abundanceof loopiness, generally looser construction with correspondinginterfilament spacing and relative absence of filamentary core in whichloops present are not visible from the outside. In simplest form, one ofthese loops approximates a crunodal plane curve, differing drasticallyfrom a helical configura tion such as may be formed by wrapping about amandrel or by twisting. Depending upon the operating conditions. variousdistortions of the loops, undulations, and configurations in the form ofprotruding or twisted bights may appear. The last of these variations,strangling of one loop by another, and any other configuration thatresists removal by moderate tensioning of the yarn are undesirable inpractice of the present invention. The easily removable loops of thetype here considered may be denoted metastable because they persist atsubstantially zero tension but become progressively distorted as thefilaments are tensioned, disappearing entirely as the filaments becomerealigned under light-to-moderate tension. Not only is this intermediateyarn containing a multitiude of metastable loops characterized by a verylow yield-point (i.e., tension at which extension to greater length isaccounted for by slippage owing to distortion or removal of loops,rather than by elastic stretching), usually no more than a fewhundredths gram per denier, but the tension required to extend the yarnto half again this intermediate length is only a few tenths gram perdenier. conceivably, even a simple monofilament could be formed intosuch a metastable configuration with sufficient overfeed of the filamentand could be maintained at substantially zero tension.

According to the present invention, the filament loops formed by passageof the yarn through the zone of fluid turbulence are stabilized byappropriate treatment here termed generally setting. Both type andintensity of setting treatment are determined by characteristics of theyarn to be treated and the conditions which it will be subjected insubsequent processing and in use as textile or other products. Aftercompletion of the setting treatment, the filament loops individuallyresist deformation, exhibiting no appreciable tendency to resume thestraight linear form of a starting filament. Apparently the internalstresses induced in the filaments by the convolution have been relievedso that the loopy form now is stable rather than metastablev Even afterbeing removed entirely by subsequent tensioning sufficient to realignthe filaments, the loops tend to return more or less completely afterremoval of the tension.

Cellulose esters, such as acetate, propionate, or acetatebutyrate, whichare relatively hydrophilic and thermoplastic, may be set satisfactorilyby steaming for several seconds at a temperature of about 100 C., whichrelieves the stresses present in the convolutions suificiently to renderthem stable. For cellulose esters and many other yarn compositions, therate of loop recovery depends to a considerable extent upon humidity andtemperature of the surroundings, and the amount or rate may be increasedby relaxation of the yarn in boiling water for several minutes; asconventional textile finishing usually contains a boil-off step, theseyarns (after stabilization of the loopy configuration) may be woven orknitted at their extended length into fabric that will acquire a greatlyincreased bulk or loft during finishing.

Most recently developed fiber constituents, even though relativelyhydrophobic, may be set thermally. The temperature and time of treatmentmay be increased over those mentioned above so as to bring about thedesired set or stabilization of the filament configuration. Among thematerials that may be set thermally are glass, vinyl polymers, nylon,and polyesters (such as polyethylene terephthalate). Of course, steamingalso may be helpful in setting nylon or other of the newer polymers. Thesetting zone is represented schematically in Figure l by tube throughwhich the yarn passes after being treated in jet 9. To avoid excessivelength of tube for setting periods of more than a minute or so, the yarnmay make several passes from end to end inside the tube over suitablerollers, or the yarn may be allowed to pile up in the tube so that itbecomes set before being withdrawn at the other end, in which case thetube need not be straight but may be .I-shaped, for example, to receivethe yarn in the body of the J and emit it through the open leg of the J.Regenerated cellulose normally requires alkaline or similar treatment toacquire a satisfactory set, and analogous treatment may be useful insetting other kinds of fiber constituents. Other methods of setting someof these and other fiber constituents may be employed.

After being set, the yarn appears essentially as it does after emergencefrom the jet, exhibiting a multitude of loops in the continuous-filamentcomponent. The yarn then is extended to distort the set loops or toremove them entirely, as desired. This is accomplished conveniently bypassing the yarn successively over a set of rolls rotating at a certainspeed and then over a subsequent set of rolls rotating at greater speed.In Figure 1, these two sets of rolls are joined by dashed lines toelement 21, which is a control mechanism of conventional design adaptedto ensure the proper rate ratio and thus the desired degree ofextension. In the set yarn the apparent yield-point, which is higherthan the yield-point of the unstabilized intermediate, is more likely ameasure of the bending modulus of a few loops as they begin to distortunder tension. The yarn customarily is Wound up at substantially theextended length because of the ease with which the extended yarn may bebackwound later, so the second set of rolls may constitute the Windup,as shown; however, a degree of recovery to shorter length may bepermitted by interposing a separate set of extending rolls and thenwinding up at a slower rate than the yarn is forwarded by the extendingrolls. The tension used to extend the yarn should not be excessive orthe recoverability may be impaired. If desired, the tension employed maybe such as to restore the yarn length to a value merely approaching theinitial length to a chosen degree.

Recovery of the extended yarn to shorter length after removal of theextending tension apparently occurs because the set configuration issufiiciently elastic to prevent the extension from constituting theextended length an equilibrium or stable configuration, instead of theset configuration. In practice, complete recovery to the set length isnot usually realized, the return being on the order of halfway orsomewhat more. While appreciable recovery normally occurs at roomtemperature, recovery to an approximation of a thermally induced set ishastened by exposure to a temperature approaching but not exceeding thesetting temperature. Swelling treatment for the yarn may be useful inaccelerating recovery. The process of this invention is exemplifiedbelow using a multifilament yarn made of nylon (polyhexamethyleneadipamide).

Example Nylon yarn containing 34 filaments of approximately 2 denier perfilament (d.p.f.) twisted one turn per inch is fed to a jet of the kindillustrated in the drawings at a speed of yards per minute (y.p.m.). Airis supplied to the jet at gage pressure of 40 pounds per square inch.The resultant loopy yarn, which looks like that shown in Figure 5 andhas a yield-point of about 0.01 gram per denier (g.p.d.) is forwardedaway from the jet at a rate of 34 y.p.m. and a tension of less than 0.01g.p.d.; the net overfeed of yarn thus is 250% or 2.5x, the difference inyarn length appearing as loopiness of the individual filaments. The yarnis passed through a chamber containing steam superheated at atmosphericpressure to a temperature of about 200 C., in which it remains forapproximately five seconds. Unchanged in appearance by this settingtreatment, the yarn then is extended 1.5x (based upon the stabilizedlength) by passage over draw rolls at a tension of 0.2 g.p.d. and iswound onto a bobbin at constant length. In subsequent i ersion inboiling water after unwinding from the bobbin, the yarn recoversapproximately 50% of the difference between the extended length and thestabilized unextended length. (Residual shrinkage of the yarn measuredon an untreated sample in boiling water is only about 7%.) The relaxedyarn appears quite fluffy and bulky, exhibiting some crunodal loops andconsiderable irregular undulation, as shown in Figure 6. The yarn may betensioned easily to the previous extended length (at least 20% over therecovered length), and upon being released it returns to substantiallythe recovered length. Socks knitted of the unrelaxed extended yarnbecome bulky and lofty during a hot aqueous finishing operation, losingabout one third of their surface area (as knit). They are quiteextensible, smooth and dry to the touch, and adapted to fit a wide rangeof foot sizes.

For best results the yarn is processed according to this invention at100% or greater net overfeed; net overfeed is the difference between therates of feeding yarn to the jet and of forwarding the set yarn ascompared to the latter rate itself. Of course, the length difference istaken up in the loopiness induced by the jet. Overfeeds of severalhundred percent and greater may be employed. Jet pressure should be aslow as practicable to avoid stable loops instead of the metastableconfiguration discussed above. Twist in the yarn should be low,preferably one turn per inch or less (to zero twist) to produce thedesired metastable intermediate yarn. With the illustrated type of jet,it normally is not necessary to exceed a supply pressure of about fortypounds per square inch (p.s.i.) gauge. When pr0cessing yarn at pressuresabove about 50 p.s.i., especially at reduced overfeed, the illustratedjet produces progressively more stable yarn configurations which areundesirable in the intermediate yarn of this invention. Usually, thequality of product is improved by concentrating overfeed downstream fromthe jet, thus minimizing windup tension. Instead of merely indicatingthe tension, which conveniently is sufficient to extend the stabilizedyarn to the length at which it will be processed into fabric, thetensiometer may control that tension through appropriate servomechanism,as by adjusting the rate of drive roll 18 downstream from thetensiometer. Of course, the rate of windup is adjusted accordinglythrough mechanism 21, which also ensures the proper extension ratiobetween drive roll 18 and the windup.

A batch process may be used instead of the illustrated continuous flow;accordingly, the yarn may be wound up on a package soon after emergencefrom the jet (be fore stabilization) or may be placed loosely in acontainer, the package or container being used to support the yarnduring the setting treatment, after which the yarn may be backwound,extended, and rewound or otherwise processed in analogous fashion.Packaging of the stabilized loopy yarn before extension may not beworthwhile because of the likelihood of entanglement of loops inadjacent wraps of yarn. Whether the process is continuous ordiscontinuous the equipment, except for the jet and possibly the settingtube, is conventional yarnprocessing apparatus.

No configuration assumed by yarn processed according to this inventionis dependent upon residual shrinkage in the yarn, as may be induced bystretching or other treatment. In fact, shrinkage is undesirable,particularly in the setting step, because tightening of the loops mightrender the set yarn difiicult or impossible to extend as desired withoutbreaking or other damage to the yarn. Nor does this processing involveany stretching or colddrawing of the yarn; the extension step dependsupon distortion of the loopy configuration to produce the increasedlength. Whereas the length of the intermediate yarn (downstream from thejet before extension) is at most half the initial length, preferablyless, extension of the stabilized intermediate should bring the lengthto at least half again the intermediate length and preferably at leasttwo thirds the initial length. After extension, the yarn should recoverat least halfway to the intermediate length. Subsequent extension andrecovery between these limits under moderate and very slight tensions,respectively, may be expected to be substantially complete. Of course,yarns of some thermoplastic materials exhibit appreciable creep ordelayed recovery ,under ordinary room conditions, so measurementimmediately after release of an extending force may not reveal the fullrecoverability, whether of yarn or fabric produced therefrom. Theprocessing conditions, such as air presure, amount of overfeed, andsetting treatment, can be varied to impart the desired characteristicsto the yarn.

Although perhaps at their best in knit fabrics, such as sweaters andsocks, in which the yarns are less confined than in most woven fabrics,the yarns (and fabrics) of this invention are also useful in themanufacture of form-fitting woven apparel, such as swim-suits andvarious undergarments. Fabrics comprising these yarns should recover tothree quarters or less of their extended length. The bulk and coveringpower of fabrics consisting entirely of continuous filaments areenhanced greatly by processing of the yarns according to this invention,and the slick handle often associated with such fabrics is replaced by apleasantly soft and dry feel. Many advantages of practicing theinvention upon yarns of all kinds are apparent. Notably, yarns treatedaccording to this invention do not have to be plied, as do yarns relyingupon helical twist for their extensibility and recoverability.

What is claimed:

l. Process comprising passing thermoplastic continuous filament yarnhaving a twist of less than about one turn per inch at a fixed rate intoa zone of fluid turbulence sufficient only to convolute the filamentsindivid' ually into a multitude of crunodal loops along the lengths offilaments, whereby internal stresses are induced in the filaments, saidloops being only loosely intermingled such that the yarn has a yieldpoint of less than 0.05 gram per denier; removing the filaments in abundle as a selfsupporting yarn from the zone of fluid turbulence atsubstantially zero tension and at a rate of less than half the fixedfeeding rate; stabilizing the loops by exposing the yarn to astress-relieving treatment; tensioning the yarn to remove a substantialnumber of the loops; and relax ing the yarn to provide an elastic yarncharacterized by extensibility under very slight tension.

2. The process of claim 1 in which the yarn is a nylon yarn.

3. Yarn comprising continuous thermoplastic filaments exhibitingcrunodal loops along the lengths of filament, said loops being looselyintermingled so that the yarn is characterized by extensibility undervery slight loop-distorting tension to at least one fifth again theunextended yarn length and by recoverability to substantially theunextended length upon removal of the tension.

4. Yarn comprising continuous thermoplastic filaments exhibiting amultitude of internally relieved crunodal loops along the lengths offilament, said loops being only loosely intermingled so that the yarn ischaracterized by extensibility under very slight tension to a yarnlength at least half again the unextended length and by recoverabilityto a length at most the arithmetic mean of the extended and unextendedlengths.

5. The product of claim 4 in which the yarn is a nvlnn yarn.

References Cited in the file of this patent UNITED STATES PATENTS2,379,824 Mummery July 3, 1945 2,413,123 Underwood Dec. 24, 19462,414,800 Charch Jan. 28, 1947 2,564,245 Billion Aug. 14, 1951 2,604,689Hebeler July 29, 1952 2,638,146 Rounseville et al. May 12, 19532,671,745 Slayter Mar. 9, 1954 2,783,609 Breen Mar. 5, 1957 2,807,862Griset Oct. 1, 1957 FOREIGN PATENTS 520,934 Belgium Dec. 24, 1953558,297 Great Britain Dec. 30, 1943

